Bacteria and other microbes can be used to \"clean up\" an oil spill by breaking

Question

Bacteria and other microbes can be used to "clean up" an oil spill by breaking down oil into carbon dioxide and water. Two samples isolated from the Deepwater Horizon leak in the Gulf of Mexico were labeled A and B. The DNA of each was isolated and the percent thymine measured in each sample. Assume the organisms contain normal double-stranded DNA and predict the composition of the other bases. Sample A contains 19.3% Thymine Sample B contains 31.7% Thymine Number Number % A % A Number Number %G Number Number %) C Both samples are then denatured to remove the secondary structure. Which l have the higher temperature to denature?

Explanation / Answer

Chargaff's rules state that DNA from any cell of all organisms should have a 1:1 ratio (base Pair Rule) of pyrimidine and purine bases and, more specifically, that the amount of guanine should be equaled to cytosine and the amount of adenine should be equal to thymine.

A+G+C+T= 100 & A=T and C=G

So in sample A, as A=T=19.3

C+G=100- 38.6=61.40

Therefore C=G=30.70

In sample B, T=A=31.7%

Therefore C=G=18.30

Each species of DNA has a characteristic denaturation temperature or melting point: the higher its content of GC base pairs, the higher the melting point of the DNA. This is because GC base pairs, with three hydrogen bonds, are more stable and require more heat energy to dissociate than A=T base pairs

As sample A has 61.40% oF G+C, so the sample A will have higher temperature to denature

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